Dehydration Dent

Suddenly confronted with a significant dent in my forehead I of course turned to the internet. Information was sparse, but I did find one post that documented a similar forehead dent that turned out to be caused by dehydration. I tested this hypothesis by drinking a ton of water and sure enough, within an hour or so the dent was receding and by the morning my forehead was normal.
In retrospect I realized I had not been drinking enough water for the preceding few days. First as a result of two days of driving, but followed with a bunch of hiking in hot weather.
Lesson learned!
Here's a link to the post that helped me out.  How dehydration causes skin deformities